The risk of disruptive climate change grows every day. John Holdren, the White House science advisor, said last year that we have three options: Mitigate, adapt, suffer. If we don’t mitigate (meaning reduce emissions), we’ll have to adapt (move to new places, develop new crops, build sea walls). If we do neither, we’ll suffer. But, as regular readers of this blog know, there’s a fourth option–geoengineering.

Geoengineering is term used to describe planetary-scale technologies that are designed to counteract the climate effects of past greenhouse gas emissions to the atmosphere. I’ve been fascinated with geoengineering for about two years, and this week FORTUNE will publish my story, The Business of Cooling the Planet, about three startup companies that want to save the planet by capturing carbon dioxide from the air. This topic is so important that I’m planning to expand the story into a short e-book in the next couple of months.

The FORTUNE story begins by describing how Microsoft founder Bill Gates became an expert on climate and energy:

One of the cool things about being Bill gates is that if you are curious about something, you can find smart people who will teach you whatever it is that you want to know. About five years ago Gates decided that he wanted to learn about climate change, so he arranged for two of the world’s leading climate scientists, David Keith of the University of Calgary in Alberta, Canada, and Ken Caldeira of the Carnegie Institution, to organize a series of seminars. Since then, Keith and Caldeira have recruited scientists, energy experts, economists, and policy wonks to deliver about a dozen detailed presentations to Gates. He prepares by doing hundreds of pages of reading, some quite technical; the ensuing discussions, which last three or four hours, can be intense. “Bill has the intellectual curiosity of a very bright graduate student,” Caldeira says, “but a graduate student whose time you are not supposed to waste.”

This is no academic exercise. Gates has been convinced that the risk of global warming is worse than most people think. He can see that the world’s governments have failed to curb the emissions caused by burning coal, oil, and natural gas. In June 2010 he put together a coalition of business leaders, including GE’s Jeff Immelt, to urge Congress to invest more in clean-energy research, but that’s not happening. So the Microsoft billionaire and philanthropist has stepped into the breach to become the world’s leading funder of research into geoengineering— deliberate, large-scale interventions in the earth’s climate system intended to prevent climate change and its repercussions.

Since 2007, Gates has given about $4.6 million of his money to Caldeira and Keith for geoengineering research. Intellectual Ventures, a private company funded in part by Gates, has explored such technologies as building an 18-mile-long hose, tethered by balloons, that would spray tiny particles into the stratosphere to block the sun’s rays. Gates has even attached his name to a patent application for ocean-churning technology designed to sap the strength of hurricanes, which appear to be getting fiercer because of global warming.

The story goes on focus on three startup companies that are working on

A straightforward, albeit audacious, way to cool an overheating planet: Build many thousands of big machines to remove carbon dioxide from the air.

Geoengineering — deliberate, planetary-scale efforts to counter the impact of climate change — is so controversial that a high-powered 18-member Washington task force that spent almost two years studying the idea couldn’t decide what to call it.

Most want to rename it “climate remediation.” A few want to stick with geoengineering. But all agreed that, whatever you call it, the U.S. government should begin “a coordinated federal research program to explore the potential effectiveness, feasibility, and consequences of climate remediation technologies.”

In a 33-page report released today in Washington, the task force of the Bipartisan Policy Center emphasized that climate remediation is not a substitute for managing the risks of climate change through mitigation (i.e., reducing emissions of carbon dioxide and other greenhouse gases, most of them generated by burning fossil fuels). It also says that no geoengineering technology is ready for deployment.

But, the group said, it’s imperative that governments, scientists and engineers learn more about geoengineering because the risks of climate change are increasing.

Mitigation measures currently being considered, regardless of their pace of efficacy, will not be able to return atmospheric greenhouse gas concentrations to pre-industrial levels for centuries…

Although we do not know exactly how much the climate will change or how fast, globally disruptive or even catastrophic results are possible…Global climate change could unfold in ways that would be very difficult to manage

In plain language: what we’re doing (or not doing) now to deal with climate change isn’t working, and the consequences of those failures are likely to be disastrous.

“I’m not sure we would have had a consensus recommendation on research if mitigation efforts were going great guns,” said Stephen Rademaker, co-chair of the task force and a former assistant secretary of state during the Bush II administration. [click to continue…]

The only thing that’s curbed carbon dioxide pollution on a scale that’s meaningful is the global recession.

This is why—unless and until scientists discover a breakthrough in clean energy or political leaders impose a global fossil-fuel tax or carbon emissions cap—we need to thing seriously about geoengineering.

Over the last decade, Nathaniel “Ned” David, a Harvard and Berkeley-trained PhD., has co-founded five technology companies that have collectively raised more than $700 million in financing. One, Syrrx, made a diabetes drug. A second, Achaogen, is developing a potent antibiotic. A third, Kythera Biopharmaceuticals, a pioneer in the field of “aesthetic medicine,” is working on an injectable drug that will reduce localized fat–no more double chins!–and it was his experience there that led Ned into the world of clean energy and climate change.

There’s nothing wrong with helping people to look better, he told me when we met recently, but it wasn’t enough: “I was feeling a little ennui around what I was doing.” His son, Magellan, had just been born. “I suddenly had this desire to work on something of great moral urgency,” he said.

Ned David

That’s no longer an issue. Ned, who is a boyish 43, helped start Sapphire Energy, an algae company, on whose board he still sits, and last fall he became the president of an audacious San Francisco-based startup called Kilimanjaro Energy. It goal? To harvest CO2 from the atmosphere and use it to make transportation fuels with a much lower carbon footprint than gasoline or diesel.

The name of the company says it all: “We’re going to try to make fuels, while simultaneously saving the snows of Kilimanjaro,” Ned says. [click to continue…]